The prior art teaches equipping vehicles with “variable displacement,” “displacement on demand,” or “multiple displacement” internal combustion engines in which one or more cylinders may be selectively “deactivated,” for example, to improve vehicle fuel economy when operating under relatively low-load conditions. Typically, in a multi-displacement system, the engine's cylinders are deactivated through use of deactivatable valve train components, such as the deactivating valve lifters as disclosed in U.S. patent publication no. U.S. 2004/0244751 A1, in which a supply of pressurized engine oil is selectively delivered from an engine oil gallery to a deactivatable valve lifter through operation of a solenoid valve under the control of an engine control module.
With the intake and exhaust valves of each deactivated cylinder remaining in their closed positions during engine operation in the cylinder-deactivation mode, combustion gases are trapped within each deactivated cylinder, whereupon the deactivated cylinders operate as “air springs” to reduce engine pumping losses. When vehicle operating conditions are thereafter deemed to require an engine output torque greater than that achievable without the contribution of the deactivated cylinders, as through a heightened torque request from the vehicle operator (based upon a detected position of the vehicle's accelerator pedal), the deactivatable valve train components are returned to their nominal activated state to thereby “reactivate” the deactivated cylinders. More specifically, under one prior art approach,
Preferably, the engine control module operates the solenoid valve such that the lifter's locking pins are moved between their respective locked and unlocked positions as the lifter's cam lies on the base circle of its corresponding cam surface, thereby minimizing lifter wear and noise. Thus, the triggering of the oil control solenoids is preferably synchronized either to the crankshaft in a pushrod engine, or the cam shaft in an overhead cam engine.
It is also known that, at each engine speed, there is a range of potential solenoid trigger points that produce a proper sequencing of the deactivatable valve train components, with the deactivation triggering window being significantly “wider” than the reactivation window because less time is needed to increase the oil gallery pressure to the relatively-lower unlatching pressure, as opposed to dropping the oil gallery pressure from a relatively-higher sustained pressure down to the latching pressure. Further, it is known that a hydraulic delay exists in a multi-displacement system between the commanded hydraulic control and the actual response, I.e., the change in the solenoid's state and the corresponding change in the state of the hydraulically-deactivatable valve train component, as the control pressure increase or decrease propagates from the solenoid to the component.
The prior art has sought to provide the engine control module with an estimation of this hydraulic delay, for example, by mapping computer-modeled and empirically-confirmed hydraulic response times in a lookup table as a function of oil pressure and estimated oil aeration. However, to the extent that a multi-displacement system is characterized both by a generally negligible oil pressure impact on hydraulic delay over the engine's nominal operating range, as well as a generally negligible amount of oil aeration at normal engine operating speeds, the prior art approach will fail to provide the required time-based hydraulic delay estimates. Accordingly, there is a need to determine the hydraulic deactivation and reactivation control delays as a function of engine operating parameters providing a higher resolution than known methods based on oil pressure and estimated oil aeration.